Which component helps ensure that nodes in a Cassandra cluster are aware of each other's states?

The Gossip Protocol is the key component in Cassandra that allows nodes within a cluster to communicate and share state information with one another effectively. This decentralized protocol enables each node to learn about the presence and status of other nodes in the cluster, facilitating data replication and consistency.

The primary function of the Gossip Protocol is to disseminate information regarding the health and availability of nodes, as well as to keep track of the data and services that each node is responsible for. By using a probabilistic approach, nodes regularly exchange state information in a gossip-like manner, which ensures that even if a node fails or temporarily becomes unreachable, the other nodes can still maintain an accurate understanding of the cluster's topology and node statuses.

In contrast, Memtables and SSTables are related to data storage operations. Memtables are in-memory data structures used for writing data before it is flushed to disk as SSTables, which are immutable files that store the actual data in a column-family format. The Compaction Strategy refers to how Cassandra manages the merging of SSTables to optimize read performance and reduce disk space usage. While these components are essential for data management, they do not play a role in maintaining awareness of the state of nodes in the cluster.